Mon·Sep 28, 2015Monday·September 28, 2015

1. 01*

   Radiative energy loss and radiative p_T-broadening of high-energy partons in QCD matter

   Bin Wu🇫🇷

   I give a self-contained review on radiative p_T-broadening and radiative energy loss of high-energy partons in QCD matter. The typical p_T^2 of high-energy partons receives a double logarithmic correction due to the recoiling effect of medium-induced gluon radiation. Such a double logarithmic term, averaged over the path length of the partons, can be taken as the radiative correction to the jet quenching parameter qhat and hence contributes to radiative energy loss. This has also been confirmed by detailed calculations of energy loss by radiating two gluons.

   hep-phhep-exnucl-exnucl-thNucl.Part.Phys.Proc.(2016)·3 citations
2. 02*

   $J_{E_T}^{\mathrm{II}}$: A Two-prong Jet Finding Algorithm

   Yang Bai🇺🇸 · Zhenyu Han🇺🇸 · Ran Lu🇺🇸

   We propose a new global jet-finding algorithm for reconstructing two-prong objects like hadronic weak gauge bosons at a hadron collider. The selection of particles in a two-prong jet is required to maximize a $J_{E_T}^{\mathrm{II}}$ function, which contains a modified second Fox-Wolfram moment and prefers a two-prong structure for a fixed jet mass. Compared to the traditional jet-substructure method, our algorithm can provide a similar or better performance for identifying boosted weak gauge bosons that are produced from either Standard Model processes or heavy di-boson resonance decays.

   hep-phhep-ex5 citations
3. 03*

   Dark Photons from the Center of the Earth: Smoking-Gun Signals of Dark Matter

   Jonathan L. Feng🇺🇸 · Jordan Smolinsky🇺🇸 · Philip Tanedo🇺🇸

   Dark matter may be charged under dark electromagnetism with a dark photon that kinetically mixes with the Standard Model photon. In this framework, dark matter will collect at the center of the Earth and annihilate into dark photons, which may reach the surface of the Earth and decay into observable particles. We determine the resulting signal rates, including Sommerfeld enhancements, which play an important role in bringing the Earth's dark matter population to their maximal, equilibrium value. For dark matter masses $m_X\sim$ 100 GeV - 10 TeV, dark photon masses $m_{A^{\prime }}\sim$ MeV - GeV, and kinetic mixing parameters $\epsilon \sim 10^{-10}-10^{-8}$, the resulting electrons, muons, photons, and hadrons that point back to the center of the Earth are a smoking-gun signal of dark matter that may be detected by a variety of experiments, including neutrino telescopes, such as IceCube, and space-based cosmic ray detectors, such as Fermi-LAT and AMS. We determine the signal rates and characteristics, and show that large and striking signals---such as parallel muon tracks---are possible in regions of the $(m_{A^{\prime }},\epsilon )$ plane that are not probed by direct detection, accelerator experiments, or astrophysical observations.

   hep-phastro-ph.COastro-ph.HEhep-exPRD(2016)·68 citations
4. 04*

   Possible Effects of Fierz Transformations on Vacua of Some Four-Fermion Interaction Models

   Bang-Rong Zhou🇨🇳

   A theoretical research on possible effects of the Fierz transformations on the ground states (vacua) of some 2-flavor and $N_c$-color four-fermion (quark) interaction models has been systematically conducted. It has been shown that, based on the known criterions of the interplay between the antiquark-quark ($\bar{q}$-$q$) and diquark ($q$-$q$) condensates, in 4D space-time, for the given $\bar{q}$-$q$ channel couplings with chiral symmetry and from the heavy gluon exchange, the effects of the Fierz transformations are not enough to change the feature that the models' vacua could only be in the pure $\bar{q}$-$q$ condensate phases. However, for a given pure scalar $q$-$q$ channel coupling with the strength $H_S$, the Fierz transformations will lead to the nontrivial effect that the model's vacuum could be in the expected $q$-$q$ condensate phase only if $N_c<9$ and $H_S$ is small, and as the increase of $N_c$ and $H_S$, the vacuum will get first in a coexistence phase with $q$-$q$ and $\bar{q}$-$q$ condensates then in a pure $\bar{q}$-$q$ condensate phase until $N_c\to \infty$. Similar conclusions are also drawn from relevant four-fermion interaction models in 2D and 3D space-time. The general significance of the research is indicated.

   hep-phhep-thInt.J.High Energy Phys.(2015)·0 citations
5. 05*

   Flavor tagging TeV jets for BSM and QCD

   Keith Pedersen🇺🇸 · Zack Sullivan🇺🇸

   We present a new scheme for tagging high-$p_T$ bottom and charm jets using energetic muons. Contemporary track-based $b$ tags lose their ability to reject light jet background as jet $p_T\to \mathcal{O}(\mathrm{TeV})$, where the massive boost exposes fundamental limits in tracking resolution. For our "${\mu }_x$" tag, the signal efficiency and light jet rejection is robust versus $p_T$. In the tested regime (jet $p_T\in [0.5,2.1]$ TeV), ${\mu }_x$ tags $\sim 14\%$ of $b$ jets, $\sim 6.5\%$ of $c$ jets and $\sim 0.65\%$ of light jets. Since ${\mu }_x$ tagging should be immediately useful in a searches for heavy resonances, we test it with a typical dijet search --- a heavy, leptophobic $Z^{\prime }$.

   hep-phhep-ex0 citations
6. 06*

   Collinear Twist-3 Approach to Transverse Single-Spin Asymmetry in Proton-Proton Collision

   Koichi Kanazawa🇺🇸 · Andreas Metz🇺🇸 · Yuji Koike🇯🇵 · Daniel Pitonyak🇺🇸

   We present our recent analysis on the transverse single-spin asymmetry (SSA) in inclusive pion and direct-photon production in pp collisions for RHIC kinematics. The analysis includes the contributions from twist-3 quark-gluon-quark correlations in the proton and twist-3 fragmentation effects for the pion. Some of the functions appearing in the formula for the SSA, such as the soft-gluon-pole Qiu-Sterman function, the nucleon transversity, and the Collins function were fixed consistently with the SSA data in semi-inclusive DIS and in e+e- annihilation, so that our analysis is free from the sign mismatch problem.

   hep-phhep-ex0 citations
7. 07*

   Dynamical transition between two mesons and a tetraquark

   I. A. Toledano Juarez🇲🇽 · G. Toledo Sanchez🇲🇽

   We consider a system composed of two identical light quarks ($qq$) and two identical antiquarks ($\bar{Q}\bar{Q}$) that can be linked either as two mesons or as a tetraquark, incorporating quantum correlations between identical particles and an effective many-body potential between particles. We perform a 3-D Monte Carlo simulation of the system, considering the configurations allowed to form: i) Only two mesons, ii) Only tetraquark and iii) two mesons and tetraquark . We characterize each case and determine whether it is energetically more favorable to form a tetraquark or two mesons, as a function of the interparticle separation distance which, for a fixed number of particles, can be identified as a particle density. We determine how the two mesons, which dominate the low density regime, mixes with a tetraquark state as the density increases. Properties like the mean square radius and the two-particle correlation function are found to reflect such transition, and we provide a parameterization of the diquark correlation function in the isolated case. We track the dynamical flipping among configurations to determine the recombination probability, exhibiting the importance of the tetraquark state. We analize the four-body potential evolution and show that its linear behavior is preserved, although the slope can reflect the presence of a mixed state. Results are shown for several light-quarks to heavy-antiquarks mass ratios whenever they are found to be relevant.

   hep-phnucl-thPRC(2015)·1 citation
8. 08*

   Exploring the Parameter Space of Warm-Inflation Models

   Mar Bastero-Gil🇪🇸 · Arjun Berera🇬🇧 · Nico Kronberg🇬🇧

   Warm inflation includes inflaton interactions with other fields throughout the inflationary epoch instead of confining such interactions to a distinct reheating era. Previous investigations have shown that, when certain constraints on the dynamics of these interactions and the resultant radiation bath are satisfied, a low-momentum-dominated dissipation coefficient $\propto T^3/m_{\chi }^2$ can sustain an era of inflation compatible with CMB observations. In this work, we extend these analyses by including the pole-dominated dissipation term $\propto \sqrt{m_{\chi }T}\exp (-m_{\chi }/T)$. We find that, with this enhanced dissipation, certain models, notably the quadratic hilltop potential, perform significantly better. Specifically, we can achieve 50 e-folds of inflation and a spectral index compatible with Planck data while requiring fewer mediator field ($O(10^4)$ for the quadratic hilltop potential) and smaller coupling constants, opening up interesting model-building possibilities. We also highlight the significance of the specific parametric dependence of the dissipative coefficient which could prove useful in even greater reduction in field content.

   hep-phastro-ph.COJCAP(2015)·26 citations
9. 09*

   Signatures of lower scale gauge coupling unification in the Standard Model due to extended Higgs sector

   M.V. Chizhov🇧🇬 · V.A. Bednyakov🇷🇺

   The gauge coupling unification can be achieved at a unification scale around 5 x 10^{13} GeV if the Standard Model scalar sector is extended with extra Higgs-like doublets. The relevant new scalar degrees of freedom in the form of chiral Z* and W* vector bosons might "be visible" already at about 700 GeV. Their eventual preferred coupling to the heavy quarks explains the non observation of these bosons in the first LHC run and provides promising expectation for the second LHC run.

   hep-phhep-exPhys.Atom.Nucl.(2016)·3 citations
10. 10*

    Discovery potential for $T^{\prime }\to tZ$ in the trilepton channel at the LHC

    Lorenzo Basso🇫🇷 · Jeremy Andrea🇫🇷

    The LHC discovery potential of heavy top partners decaying into a top quark and a $Z$ boson is studied in the trilepton channel at 13 TeV in the single production mode. The clean multilepton final state allows to strongly reduce the background contaminations and to reconstruct the $T^{\prime }$ mass. We show that a simple cut-and-count analysis probes the parameter space of a simplified model as efficiently as a dedicated multivariate analysis. The trilepton signature finally turns out to be able to probe $T^{\prime }$ masses up to $2.0$ TeV, when mixing with first generation quarks is included. The reinterpretation in terms of the top-$Z$-quark anomalous coupling is shown.

    hep-phPoS(2015)·0 citations
11. 11*

    Summary of the XXVIIth Rencontres de Blois: Particle Physics and Cosmology

    Gavin P. Salam🇨🇭

    This writeup summarises some of the highlights from the 2015 Rencontres de Blois, with a compression ratio of about 100:1 relative to the original presentations.

    hep-phhep-ex2 citations
12. 12*

    Undersaturation of quarks at early stages of relativistic nuclear collisions: the hot glue initial scenario and its observable signatures

    H. Stoecker🇩🇪 · M. Beitel🇩🇪 · T.S. Biró🇭🇺 · L.P. Csernai🇳🇴 · K. Gallmeister🇩🇪 · M.I. Gorenstein🇺🇦 · C. Greiner🇩🇪 · I.N. Mishustin🇩🇪 · M. Panero🇮🇹 · S. Raha🇮🇳 · L.M. Satarov🇩🇪 · S. Schramm🇩🇪 and 8 other authors

    The early stage of high multiplicity nuclear collisions is represented by a nearly quarkless, hot, deconfined pure gluon plasma. This new scenario should be characterized by a suppression of high $p_T$ photons and dileptons as well as by reduced baryon to meson ratios. We present the numerical results for central Pb+Pb collisions at the LHC energies by using the ideal Bjorken hydrodynamics with time-dependent quark fugacity. It is shown that about 25\% of final total entropy is generated during the hydrodynamic evolution of chemically undersaturated quark-gluon plasma.

    hep-phhep-exhep-latnucl-ex+1Astron.Nachr.(2015)·17 citations
13. 13*

    Physical observables in the decay ${\Lambda }_b\to {\Lambda }_c(\to \Lambda +\pi )+{\tau }^{-}+{\bar{\nu }}_{\tau }$

    Nurgul Habyl🇰🇿 · Thomas Gutsche🇩🇪 · Mikhail A. Ivanov🇷🇺 · Jürgen G. Körner🇩🇪 · Valery E. Lyubovitskij🇩🇪 · Pietro Santorelli🇮🇹

    We analyze the tauonic semileptonic baryon decays ${\Lambda }_b^0\to {\Lambda }_c^{+}+{\tau }^{-}+{\bar{\nu }}_{\tau }$ with particular emphasis on the lepton helicity flip contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization components of the ${\Lambda }_c^{+}$ and the ${\tau }^{-}$, and the lepton-side forward-backward asymmetries. We use the covariant confined quark model to provide numerical results on these observables.

    hep-phnucl-thInt.J.Mod.Phys.Conf.Ser.(2015)·7 citations
14. 14*

    Central exclusive production of pion pairs in proton-(anti)proton collisions

    Piotr Lebiedowicz🇵🇱 · Antoni Szczurek🇵🇱

    We present results for exclusive $pp\to pp{\pi }^{+}{\pi }^{-}$ or $p\bar{p}\to p\bar{p}{\pi }^{+}{\pi }^{-}$ processes at high energies. We discuss the role of new additional absorption corrections in the non-resonant Lebiedowicz-Szczurek model mediated by the pomeron and reggeon exchanges. We discuss also the role of the ${\rho }^0$ and the Drell-Söding photoproduction mechanism. We compare our predictions with recent experimental results obtained by the STAR and CDF Collaborations. We present predictions for the ALICE, ATLAS and CMS experiments. Differential distributions in invariant two-pion mass and two-dimensional distributions in proton-proton relative azimuthal angle and transverse momentum of one of the protons are presented.

    hep-phActa Phys.Polon.Supp.(2015)·1 citation
15. 15*

    Exploring double-parton scattering effects for jets with large rapidity separation and in four-jet production at the LHC

    Antoni Szczurek🇵🇱

    We present an estimation of the contribution of double parton scattering (DPS) for jets widely separated in rapidity and for four-jet sample. In the case of four-jet production we calculate cross section for both single-parton scattering (SPS) using the code ALPGEN as well as for DPS in LO collinear approach. The DPS contribution is calculated within the so-called factorized Ansatz and each step of DPS is calculated in the LO collinear approximation. We show that the relative (with respect to SPS dijets and to the BFKL Mueller-Navelet (MN) jets) contribution of DPS is growing at large rapidity distance between jets. The calculated differential cross sections as a function of rapidity distance between the most remote in rapidity jets are compared with recent results of LL and NLL BFKL calculations for the Mueller-Navelet jet production at $\sqrt{s}=7$ TeV. Our results for four-jet sample are compared with experimental data obtained recently by the CMS collaboration and a rather good agreement is achieved. We propose to impose different cuts in order to enhance the relative DPS contribution. The relative DPS contribution increases when decreasing the lower cut on the jet transverse momenta as well as when a low lower cut on the rapidity distance between the most remote jets is imposed.

    hep-phActa Phys.Polon.Supp.(2015)·0 citations
16. 16*

    Jet-Medium Interactions at NLO in a Weakly-Coupled Quark-Gluon Plasma

    Jacopo Ghiglieri🇨🇭 · Guy D. Moore🇩🇪 · Derek Teaney🇺🇸

    We present an extension to next-to-leading order in the strong coupling constant $g$ of the AMY effective kinetic approach to the energy loss of high momentum particles in the quark-gluon plasma. At leading order, the transport of jet-like particles is determined by elastic scattering with the thermal constituents, and by inelastic collinear splittings induced by the medium. We reorganize this description into collinear splittings, high-momentum-transfer scatterings, drag and diffusion, and particle conversions (momentum-preserving identity-changing processes). We show that this reorganized description remains valid to NLO in $g$, and compute the appropriate modifications of the drag, diffusion, particle conversion, and inelastic splitting coefficients. In addition, a new kinematic regime opens at NLO for wider-angle collinear bremsstrahlung. These semi-collinear emissions smoothly interpolate between the leading order high-momentum-transfer scatterings and collinear splittings. To organize the calculation, we introduce a set of Wilson line operators on the light-cone which determine the diffusion and identity changing coefficients, and we show how to evaluate these operators at NLO.

    hep-phnucl-thJHEP(2016)·107 citations
17. 17*

    Bremsstrahlung Energy Losses for Cosmic Ray Electrons and Positrons

    A. Widom🇺🇸 · J. Swain🇺🇸 · R. Srivastava🇮🇹

    Recently cosmic ray electrons and positrons, i.e. cosmic ray charged leptons, have been observed. To understand the distances from our solar system to the sources of such lepton cosmic rays, it is important to understand energy losses from cosmic electrodynamic fields. Energy losses for ultra-relativistic electrons and/or positrons due to classical electrodynamic bremsstrahlung are computed. The energy losses considered are (i) due to Thompson scattering from fluctuating electromagnetic fields in the background cosmic thermal black body radiation and (ii) due to the synchrotron radiation losses from quasi-static domains of cosmic magnetic fields. For distances to sources of galactic length proportions, the lepton cosmic ray energy must be lass than about a TeV.

    hep-phastro-ph.HE0 citations
18. 18*

    Cosmological Hints of Modified Gravity ?

    Eleonora Di Valentino🇫🇷 · Alessandro Melchiorri🇮🇹 · Joseph Silk🇫🇷

    The recent measurements of Cosmic Microwave Background temperature and polarization anisotropies made by the Planck satellite have provided impressive confirmation of the $\Lambda$CDM cosmological model. However interesting hints of slight deviations from $\Lambda$CDM have been found, including a $95\%$ c.l. preference for a "modified gravity" structure formation scenario. In this paper we confirm the preference for a modified gravity scenario from Planck 2015 data, find that modified gravity solves the so-called $A_{lens}$ anomaly in the CMB angular spectrum, and constrains the amplitude of matter density fluctuations to ${\sigma }_8=0.815_{-0.048}^{+0.032}$, in better agreement with weak lensing constraints. Moreover, we find a lower value for the reionization optical depth of $\tau =0.059\pm 0.020$ (to be compared with the value of $\tau =0.079\pm 0.017$ obtained in the standard scenario), more consistent with recent optical and UV data. We check the stability of this result by considering possible degeneracies with other parameters, including the neutrino effective number, the running of the spectral index and the amount of primordial helium. The indication for modified gravity is still present at about $95\%$ c.l., and could become more significant if lower values of $\tau$ were to be further confirmed by future cosmological and astrophysical data.

    ↳ astro-ph.COgr-qchep-phPRD(2016)·94 citations
19. 19*

    Scale-dependent gravitational waves from a rolling axion

    Ryo Namba🇯🇵 · Marco Peloso🇺🇸 · Maresuke Shiraishi🇯🇵 · Lorenzo Sorbo🇺🇸 · Caner Unal🇺🇸

    We consider a model in which a pseudo-scalar field $\sigma$ rolls for some e-folds during inflation, sourcing one helicity of a gauge field. These fields are only gravitationally coupled to the inflaton, and therefore produce scalar and tensor primordial perturbations only through gravitational interactions. These sourced signals are localized on modes that exit the horizon while the roll of $\sigma$ is significant. We focus our study on cases in which the model can simultaneously produce (i) a large gravitational wave signal, resulting in observable B-modes of the CMB polarizations, and (ii) sufficiently small scalar perturbations, so to be in agreement with the current limits from temperature anisotropies. Different choice of parameters can instead lead to a localized and visible departure from gaussianity in the scalar sector, either at CMB or LSS scales.

    ↳ astro-ph.COgr-qchep-phhep-thJCAP(2016)·233 citations
20. 20*

    Probing higher-order primordial non-Gaussianity with galaxy surveys

    Daisuke Yamauchi🇯🇵 · Keitaro Takahashi🇯🇵

    With a radio continuum galaxy survey by the Square Kilometre Array (SKA), a photometric galaxy survey by Euclid and their combination, we forecast future constraints on primordial non-Gaussianity. We focus on the potential impact of local-type higher-order nonlinear parameters on the parameter estimation and particularly the confirmation of the inflationary consistency inequality. Nonstandard inflationary models, such as multifield models, introduce the scale-dependent stochastic clustering of galaxies on large scales, which is a unique probe of mechanism for generating primordial density fluctuations. Our Fisher matrix analysis indicates that a deep and wide survey provided by SKA is more advantageous to constrain ${\tau }_{\mathrm{NL}}$, while Euclid has a strong constraining power for $f_{\mathrm{NL}}$ due to the redshift information, suggesting that the joint analysis between them is quite essential to break the degeneracy between the nonlinear parameters. The combination of the full SKA and Euclid will achieve the precision level needed to confirm the consistency inequality even for $f_{\mathrm{NL}}\approx 1.5$ and ${\tau }_{\mathrm{NL}}\approx 17$, though it is still hard for a single survey to confirm it when $f_{\mathrm{NL}}\lesssim 2.7$.

    ↳ astro-ph.COgr-qchep-phPRD(2016)·16 citations
21. 21*

    Microscopic Origin of Volume Modulus Inflation

    Michele Cicoli🇮🇹 · Francesco Muia🇮🇹 · Francisco Gil Pedro🇪🇸

    High-scale string inflationary models are in well-known tension with low-energy supersymmetry. A promising solution involves models where the inflaton is the volume of the extra dimensions so that the gravitino mass relaxes from large values during inflation to smaller values today. We describe a possible microscopic origin of the scalar potential of volume modulus inflation by exploiting non-perturbative effects, string loop and higher derivative perturbative corrections to the supergravity effective action together with contributions from anti-branes and charged hidden matter fields. We also analyse the relation between the size of the flux superpotential and the position of the late-time minimum and the inflection point around which inflation takes place. We perform a detailed study of the inflationary dynamics for a single modulus and a two moduli case where we also analyse the sensitivity of the cosmological observables on the choice of initial conditions.

    ↳ hep-thastro-ph.COgr-qchep-phJCAP(2015)·32 citations
22. 22*

    Self-similar inverse cascade of magnetic helicity driven by the chiral anomaly

    Yuji Hirono🇺🇸 · Dmitri Kharzeev🇺🇸 · Yi Yin🇺🇸

    For systems with charged chiral fermions, the imbalance of chirality in the presence of magnetic field generates an electric current - this is the Chiral Magnetic Effect (CME). We study the dynamical real-time evolution of electromagnetic fields coupled by the anomaly to the chiral charge density and the CME current by solving the Maxwell-Chern-Simons equations. We find that the CME induces the inverse cascade of magnetic helicity towards the large distances, and that at late times this cascade becomes self-similar, with universal exponents. We also find that in terms of gauge field topology the inverse cascade represents the transition from linked electric and magnetic fields (Hopfions) to the knotted configuration of magnetic field (Chandrasekhar-Kendall states). The magnetic reconnections are accompanied by the pulses of the CME current directed along the magnetic field lines. We devise an experimental signature of these phenomena in heavy ion collisions, and speculate about implications for condensed matter systems.

    ↳ hep-thcond-mat.softhep-phnucl-thPRD(2015)·117 citations
23. 23*

    Quark Hadron Duality - Recent Jefferson Lab Results

    Ioana Niculescu🇺🇸

    The duality between the partonic and hadronic descriptions of electron--nucleon scattering is a remarkable feature of nuclear interactions. When averaged over appropriate energy intervals the cross section at low energy which is dominated by nucleon resonances resembles the smooth behavior expected from perturbative QCD. Recent Jefferson Lab results indicate that quark-hadron duality is present in a variety of observables, not just the proton F2 structure function. An overview of recent results, especially local quark-hadron duality on the neutron, are presented here.

    ↳ nucl-exhep-ph3 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.